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The National Standards Authority of Ireland wishes to announce the launch of period of public consultation on a new Irish National Annex to the following European standard:

“I.S. EN 16941-1:2018 On-site non-potable water systems - Part 1: Systems for the use of rainwater”

Rainwater harvesting promotes water conservation, helps reduce flooding and storm water run off and can significantly reduce water bills for commercial entities who pay for water usage through water meter accounts.

A new European Standard I.S. EN 16941-1:2018 specifies the minimum requirements of rainwater harvesting systems which are used for non-potable applications (i.e. toilet flushing, cleaning and irrigation).

The NSAI Technical Committee for Wastewater (NSAI/TC 011) has developed guidance to aid designers of rainwater harvesting systems, which are in accordance with this new standard, to calculate the appropriate size storage tank required as part of a rainwater harvesting system, considering the climatic conditions in Ireland.

The guidance has been developed to be used for both private dwelling/domestic systems and for bespoke systems designed for sites such as schools, hospitals, and sports stadia for example.

The National Annex provides guidance on:

  • the basic and detailed calculation methods for determining the working storage capacity required when installing a rainwater harvesting system for non-potable use;
  • the appropriate 'dry period' (period without rainfall) to be used when performing the calculations; and,
  • the definitions, parameters and terminology used in I.S. EN 16941-1:2018.

The public consultation will remain open until the 19th July 2019. Full details on this revision and the mechanism for submitting comments is available from:

The NSAI Technical Committee for Wastewater (NSAI/TC 011) is always on the look out for new members. If you would like to get involved in the work of this committee, please get in touch with